JP-A-H3-178835 discloses a slide mechanism for a vehicle seat having, as shown in FIGS. 5 and 6, a C-shaped lower rail 50 fixedly disposed on a vehicle body, an upper rail 51 fixed on the seat and slidably inserted in the lower rail 50 along the longitudinal direction of the lower rail 50, and a slide lock member 60 operable to maintain the lower rail 50 and the upper rail 51 in a lock state or an unlock state.
The lower rail 50 has a bottom wall 53, a pair of side walls 52 and 52 extending from respective opposite side edges of the bottom wall 53 in a direction perpendicular to the bottom wall 53, top walls 56 and 56 extending inwardly from respective top edges of the side walls 52 and 52, and dependent walls 54 extending towards the bottom wall 53 from respective edges of the top walls 56 and 56. The upper rail 51 is anchor-like shape in cross-section and has an upright wall 57 lying perpendicular to the lower rail 50 and a pair of U-shaped walls 55 and 55 branched from the upright wall 52 and received in the lower rail 50.
The vertical wall 52 of the lower rail 50 is provided with a plurality of openings 61 arranged in the longitudinal direction. The U-shaped wall 55 of the upper rail 51 has a hook portion provided with a plurality of openings 62. The lock member 60 has three claws 63 which are adapted to simultaneously engage with the openings 61 and 62 of the lower rail 50 and upper rail 51, so that the longitudinal slide movement of the upper rail 51 relative to the lower rail 50 is locked.
With the above construction, when a tensile force, for example, from the seat belt, is applied to the upper rail 51, the upper edge 55a of each of the paired U-shaped walls 55 and 55 is brought into engagement with an inside surface of the corresponding top wall 56, so as to support the upward load applied to the upper rail 51. Therefore, in order to ensure a sufficient supporting strength against such upward load, it is necessary to increase the thickness of the lower rail 50 and the upper rail 51. Thus, the conventional seat slide mechanism has a problem that the weight is increased and the production cost is high. Additionally, since the lock member 60 is designed to rotate about an axis, it is necessary to ensure a space for the rotation thereof.
The present invention has been made to overcome the problems of the conventional technique.